Manning (2011): accuracy at sentence level is quite low: 55-57%.
Horsmann et al. (2015) survey many existing tools for POS tagging English.
- Manning, C. D. (2011). Part-of-speech tagging from 97% to 100%: is it time for some linguistics?. In Computational Linguistics and Intelligent Text Processing (pp. 171-189). Springer Berlin Heidelberg.
- Tobias Horsmann, Nicolai Erbs, and Torsten Zesch. "Fast or Accurate?–A Comparative Evaluation of PoS Tagging Models."